In various situations it is desirable to identify a munitions threat such as sniper fire, rocket propelled grenades (RPGs), mortars, and man-portable air defense systems (MANPADs). Such detection systems may be used so that countermeasures may be deployed. In warfare identification may include a location so that troops may be deployed to counter the threat.
Various systems have been used to detect threats. Such systems include optical and acoustic-type systems. Acoustic techniques are generally low cost. Such systems are typically effective at only a short range. Optical techniques tend to be much faster and have a longer range but at a higher cost. For threats that are several hundred meters away, optical systems are required.
Current optical detection systems use focal plane arrays (FPA) that scan at a frame rate of 30 to 60 Hz. This frame rate corresponds to between 16 and 33 milliseconds. Such a time period, however, is not fast enough for detection of transient signals such as sniper fire, which is believed to have a duration of about 2 milliseconds. Therefore, tradeoffs may need to be made in that the detection time window needs to be shortened to improve the signal-to-noise ratio. Shortening the time window may allow events to be missed. A long time window, or a long integration time may be chosen but may reduce the probability of detection because of increased clutter. Therefore, a balance must be chosen to detect particularly short duration events. Sniper detection has the shortest duration and the weakest signal of the four above-mentioned threats.
Therefore, it would be desirable to provide an optical detection system that responds to relatively quick threats such as sniper fire as well as identifying other types of threats with a reasonable cost device.